There should be a hollow bolt running through the center of the radar reflector.
This attaches to plastic disk that thas a treaded plate which the hollow bolt attaches to. I bolted the platic plate onto my A frame and then bolted the cyclops down onto the base plate.
Other wise find the correct nut size get that welded onto a plate and bolt that to the hard top and put a spacer to support the unit.
If you are missing the base plate then I would suggest you call cyclops
They were very helpful to me, does your unit when turned upside down make a clunk ? if so definately give them a call, they had a bad glue batch back in the early 90's which they have repaired most and the others my old company bought and through away when they didn't fit what they bought them for, I got one but was too slow to save other 30 units!!